Pteropus rufus, Madagascar's largest endemic fruit bat, is widely distributed but declining in number due to habitat loss and over-hunting. The roost of Berenty, located in a 250 ha remnant of gallery forest surrounded by 30,000 ha of sisal plantations and patches of endemic spiny forest, is the largest in southeastern Madagascar and is an important historical breeding site for this species. Compared with conspecifics elsewhere in Madagascar the diet of P. rufus at Berenty is narrow, containing only 17 plant species. Seven gallery forest and four cultivated species are consistently utilised by the bats, but no endemic spiny forest species were identified in their diet. Pollen of Agave sisalana, present in 84% of faecal samples, contains 36% protein, the main digestive extraction of which was high (73%). Native fruits provide more protein that cultivars, but the latter have significantly higher concentrations of soluble carbohydrates. P. rufus has high mean buccal extraction for nitrogen (73%); carbohydrates (86%); condensed tannins (46%) and phenolics (24%). However, contrary to expectation condensed tannin extraction had no significant effect on nitrogen extraction. P. rufus swallows more viable than non-viable Ficus seeds. In 92% and 58% of germination trials, bat-passed seeds had the highest percentage germination and fastest rate of germination, respectively, compared with seeds from ripe fruits, ejecta pellets or faeces of other frugivores. A minimum foraging range of 17 km was established. The role of P. rufus in pollination is inferred from the presence of pollen on the head and thorax of bats and in their faeces. P. rufus is therefore, an important seed disperser and potentially important pollinator. However, at Berenty its' heavy reliance on the introduced cultivator A. sisalana, unique among the Pteropodidae, suggests that without this resource the remaining gallery forest could not support such a large colony of P. rufus.